Wild fish and other aquatic organisms as feed in aquaculture in Europe 243
Köster and Möllmann, 2000). Juveniles of saithe, cod and whiting may also experience
competitive interactions with Norway pout (Albert, 1994). As the abundance of the
larger predatory gadoids has been reduced to low levels, the industrial feedfish that
prey on their juveniles and eggs may now be exerting a higher level of mortality than
previously, and may potentially affect gadoid stock recruitment and slow recovery.
However, it should be noted that such profound trophic impacts are difficult to verify,
given the lack of information and the confounding effect of other impacts.
Genetic impacts
Overfished populations may exhibit the “Allee effect”. This is an inverse density
dependence at low densities, e.g. the per capita birth rate declines at low densities.
The primary factors involved in generating inverse density dependence include genetic
inbreeding and loss of heterozygosity and demographic stochasticity, including sex
ratio fluctuations (Courchamp, Clutton-Brock and Grenfell, 1999). Common factors
behind the Allee effect are not of a genetic nature and can include gregariousness,
sperm competition, cultivation effects, etc.
The genetic viability of a stock is harmed if a stock collapses and recovers, due to
the reduced number of genes in the population. However, Stephenson and Kornfeld
(reported in Beverton, 1990) concluded that the Georges Bank herring, which
reappeared after a collapse in 1977 to 1/1000th of the 1967 peak of over 1 million tonnes,
have an unchanged genetic constitution. This result may be an artefact of the limited
DNA technology of the time.
Teleost feed-fish species are characterized by a tendency to shoal. Fishing pressure
causes shoaling fish to reduce their range and maintain the same average school
size (Ulltang, 1980; Winters and Wheeler, 1985). Consequently, there can be a high
number of individuals in a shoal that may lead to a high level of genetic diversity
within the shoal (Ryman, Utter and Laikre, 1995). The next question is what size can a
genetically distinct shoal/or population be reduced to and still recover. Beverton (1990)
calculated that the smallest population size that a collapsed population dropped to and
subsequently recovered is in the order of a million fish, but local density has to play a
role.
4 .2 Criteria and indicators presently used to measure the sustainability of
reduction fisheries
The FAO Code of Conduct for Responsible Fisheries (CCRF), adopted in (FAO,
1995), aims to ensure that the right to fish “carries with it the obligation to do so in
a responsible manner so as to ensure effective conservation and management of the
living aquatic resources”. Together with its Technical Guidelines for implementation
and the other international fisheries instruments developed and adopted within
its framework (e.g. International Plan of Action for Reducing Incidental Catch of
Seabirds in Longline Fisheries, IPOA-Seabirds; International Plan of Action for the
Conservation and Management of Sharks, IPOA-Sharks; International Plan of Action
for the Management of Fishing Capacity, IPOA-Capacity; International Plan of Action
to Prevent, Deter and Eliminate Illegal and Unreported and Unregulated Fishing;
IPOA-IUU fishing), the CCRF is now widely recognized by governments and non-
governmental organizations (NGOs) as the global standard for setting out the aims
of sustainable fisheries and aquaculture over the coming decades and as a basis for
reviewing and revising national fisheries legislation.